I see in the tutorials references to the Base Station and Rover, and I understand the role of each. Would a Base Station as described be roughly the same as a stand-alone CGPS station? If yes, how is it different?
Any recommendations for which receiver (and antenna) I should buy for such a station?
Is there a tutorial on how to build a CGPS station up on the site? Or any suggestions on which one would be a close fit?
Looks like it would be very much like a CORS, ie you record/archive RINEX data perhaps on hourly/daily files, and you could subsequently post-process that against other similar stations and quantity the relative movement of one vs the other(s)
For options, these 3 currently occupy the bottom, middle, and top portions of our RTK product spectrum: RTK PostCard (~$210 with its shield) RTK Reference Station (~$699) RTK Torch which is in-stock (~$1499), you may also look at the RTK mosaic-x5 (~$1199) if you can wait a bit
I’m thinking PPP would have a better chance, since the OSR method used by a nearby CORS Network would experience similar tectonic plate drift as @Jimob’s proposed monument.
PPP doesn’t rely on anyone else’s work or performance. You basically only have to work on minimizing your own systematic errors, IMHO.
The inexpensive route would be a PostCard, a L1/L2/L3 Antenna, and a homemade ground plane.
You can install a very reliable monument with a 2" hand auger, PVC pipe for casing, and a long piece of FRP Rebar. You can even “wash” the casing into the ground with a pressure washer if you don’t have access to an extendable hand auger. Once complete, most of the Rod is inside the empty pipe casing. You will be monitoring the movement of the bottom of the rod in the earth where it’s “tipped”. The fiberglass rebar has a much lower coefficient of thermal expansion, so it’s length wont change as much with the seasons. You want to go deep to get away from possible clays with their shrink/swell protentional due to moisture changes near the surface, and far away from the frost line.
If the budget allows, spend it on the antenna upgrade first, then the GNSS device.
In the end, you also have the most reliable (positionally speaking) reference station around, with the data to update the base coordinates quarterly if you wanted.
Wow, you guys confirmed i’m in the right place! My homework for tonight is looking up all the acronyms and check out the product options you all mentioned.
The mosaic-X5 has a nice feature in that it can log RINEX data directly to SD card, and can automatically open a new log file after 6hours / 24 hours etc… The duration and message interval are configurable. You need to do the logging configuration through the X5’s internal web page, but it is fairly intuitive. The maximum SD card size is 32GB, but that should keep you going for a while…
Two years ago, i started my cgps journey with a low-res gps station using an Adafruit gps breakout board. This was a great trainer for me and threw me into the details around linux’s gpsd, python (yup… a DIY’er), and accuracy . It was apparent there was no amount of low-res position averaging that would produce a highly accurate position. The data was all over the place. Even applying IQR to toss out the outliers didn’t fix this. So yes, time to up my game.
@clive1, it is great to see there is a name for this (CORS) and added to my list.
@rftop, i will definitely check out PPP as an approach. And from what I understand of PPP, it’s “send observations, then get the exact location” email… right?
@TS-RUSSELL , thanks for the product list. The RTK Postcard sounds like a good starting point with definitely a good Antenna. As implied by @rftop, and in the ham radio parlance, “if you are going to spend money, spend it first on the antenna”.
@PaulCZ, any thoughts on the availability of the “mosaic-X5’ product? Or is this more a question for @TS-RUSSELL?
Since we’re dealing with slicing-up a millimeter for the position, you can see why the antenna is the key
I have a few product suggestions in mind, but I’m interested in finding out a few more details.
How autonomous of a setup are you looking for?
IE: will you pull the SD card once a week and manually upload the daily files to an online PPP service, DIY with RTKLIB, or do you want the Device to handle everything automatically?
Are WiFi or LAN available to the proposed monument site you’ve chosen?
How easy will your power provisions be? Do you have power near the proposed monument site? Is POE an option? Or are you planning for Solar & no comms?
Is the site completely open to the sky, no close buildings or trees, etc ?
Since you’ve already mentioned things like Python, you can absolutely be successful in this project.
The L1/L2/L5 devices offered by Sparkfun have the inherent capability. Online PPP service is Free. You can write the code to automate the file transfer if you wish.
Thanks to everyone for your thoughts and comments. So, after 2+ weeks of reading and deep diving into a myriad of details, this is where i am… with questions, of course:
Since i am interested in tectonic movement, the key priority for my cGPS station is precision of relative movement over time versus the absolute accuracy of position. Would this decision impact my analysis approach (see #4 below)?
While i am reluctant to plunk down a lot of $$$ for the receiver, i am thinking the RTK Mosaic X5 is my best bet since it has higher performance and all the components and features that i think I need.
I live in an HOA on a small lot and am thinking the antenna mount needs to be fixed up on the roof so I get 30deg of sky visibility. My biggest issue is the antenna coax run to the garage will be more than the 10m cable that it comes with. Would adding another 10m extender cable significantly reduce the signal quality and essentially offset the benefit of buying the Mosaic X5?
Analyzing the data… while RINEX post-processing with CSRS-PPP should yield better precision, would RINEX with custom python processing be a reasonable starting point to give me useful results and better insight into the overall correction/analysis process? I suppose i could start with this and switch to RINEX+PPP later. Up or downside with these options?
EDIT: how RF-sensitive is the Mosaic X5 receiver? My proposed roof-top gps antenna site is on the chimney and about 4ft from a VHF/UHF ham antenna (50w out max). Will this work or do i need to pick another location for the gps antenna?
It would be a much better idea to have base station receiver connected to the antenna as close as possible (e.g., with a short semi-rigid patch cable). Then run power and digital interface down from the roof.
My biggest issue is the antenna coax run to the garage will be more than the 10m cable that it comes with. Would adding another 10m extender cable significantly reduce the signal quality and essentially offset the benefit of buying the Mosaic X5?
I regularly run 30m+ meters of RG58 extension to do product videos and demos, with 20m as the standard run to our array of test antennas, including the benchmark USACOLNIW2. While you will loose a few dB, the signals are still strong enough, and the mosaic-X5 is sensitive enough, to capture the raw signal data needed for PPP. Opposite of @Bushman_K, I would recommend getting the receiver as close to your desk as possible, or at least have very easy access to it in case it needs attention.
I think your solution is sound. mosaic-X5, with lots of logging, will allow you to chose the best path in the future, whether that’s CSRS-PPP or other. I can’t say much about the proximity to your HAM antenna. GNSS signals, by design, should have minimum crosstalk. But 50W is a lot! And you didn’t specify what frequency you’re operating at. I would air gap that as much as is reasonable but testing should show pretty quickly if there are any issues.
The cable causes a TIME DISPLACEMENT, not a POSITION DISPLACEMENT
The receiver is looking at the GNSS signals incident on the antenna’s Phase Center, and then that all uniformly chases down the cable at the SoL.
Most receiver’s have a way to modify and account for antenna cable length, and 1PPS/TIMEPULSE cable length for time domain applications, ie cellular, telco switch, electrical phase/frequency alignment.
The PPP methods are going to solve for time error/biases, and aligning instance in time for the raw measurements at Base and Rover, as each will have their own bias and drift in their local clocks.
I’m not sure why you are telling me all that about time displacement in all caps, I know how it works.
My main reason for saying what I said is much simpler: signal level loss, nothing more and nothing less. On the other hand, a properly set-up receiver doesn’t need to be fiddled with every five minutes.
I agree with @clive1 and @sparky’s comments.
I’ve commissioned and operated CORS stations.
Properly selected coax and placing the receiver where you want/need it is how this is Professionally performed in real life
For specificity, emphasis, and the much broader audience who get here with different situations and priorities that may not have considered how it impacts different contexts.
I guess I should have chosen the other Reply button.
Most commercial GNSS antenna’s of any merit these days have enough gain to put 100’s of feet up a tower with little consequential impact on the receiver’s ability to pull the gold codes out of the noise floor. Perhaps if the antenna had 9 dB of gain I’d worry, but with high 20’s into the 30’s you’re likely to have a lot of margin for the length/quality cable you choose to run.
I’d definitely chose to run the coax, and put the receiver somewhere managable and safe.
I might be an “old-school”, but RG58 has more than 20dB of attenuation per 100ft, and even 10dB of difference could easily translate into 5-8 fewer satellites used for calculating a solution (if the signal level mask is set, which is a good practice), especially in unfavorable weather conditions. Indeed, modern “super-sensitive” receivers and high-gain active antennas are great, but a better signal level is still beneficial. While the benefits of having easy physical access to a receiver is only important until all the settings are settled.
The CNO (Carrier to Noise) is in dB/Hz not directly equivalent to dB in gain/loss in the cable at ~1.5 GHz. It’s more a figure of merit related to the correlator binning of the PRN, and how far from on-time the signal is spread across the bins and the counts in each.
The threshold to demodulate the navigation data sub-frames in GPS is around 32 dB/Hz, but the gold codes are trackable into the teens, even for some receivers in the mid 1990’s
Cable length and quality is clearly an issue, and here it’s a balance for the gain of the antenna to compensate for the cable, connectors, etc.
The bigger battle is what the antenna can see of the sky, your line-of-sight for 25,000 km and it’s placement to achieve that goal. Amplifier gain can’t fix bad antenna situation. Cabling can get it to a place that’s more suitable.
And it’s not necessarily physical access, it’s getting power to a location, and being dry, safe and secure. In many commercial situations they are going to want things in phone/tech closest, and not going to be keen to run new electrical service to odd places.
That’s not to say you can’t use a short cable and a cabinet on your roof or deck, people should do what’s practical for them. I have my antenna farm on the roof and in the yard, and my gear in my dry basement.
